Technical Field
The present disclosure relates to a semiconductor device, a battery monitoring system, and a semiconductor device diagnosing method.
Related Art
Battery monitoring semiconductor devices for monitoring/controlling a battery cell are known. Examples of such battery monitoring semiconductor devices include battery monitoring integrated circuits (ICs) for monitoring/controlling a battery cell installed in a vehicle or the like.
In such battery monitoring IC, a battery voltage at a high potential side of a battery cell and a battery voltage at a low potential side of the battery cell a compared using a comparison section such as an analog level shifter, and a battery voltage of the battery cell is measured based on a difference between both of these voltages. Here, the accuracy of the battery voltage measurement can be improved by inputting the battery voltage to the comparison section through a buffer amplifier.
The input voltage input from the high potential side of the battery cell (the highest potential side in cases including plural battery cells) subject to monitoring is sometimes used as the power supply voltage that drives the buffer amplifier of the battery monitoring IC employed. In such cases, an offset voltage arises in the output voltage of the buffer amplifier, and the accuracy of the battery voltage measurement may decrease.
Japanese Patent Application Laid-Open (JP-A) No. 2011-232161 discloses a battery monitoring IC provided with a boosting circuit that boost an input voltage. In the technology described in JP-A 2011-232161, an offset voltage arising in an output voltage of a buffer amplifier is suppressed, and the accuracy of battery voltage measurement is increased, by driving the buffer amplifier with a power supply voltage boosted from the input voltage by the boosting circuit.
In recent years, demand has increased for such battery monitoring ICs to be equipped with functionality to diagnose internal circuitry and the like. Japanese Patent Application Laid-Open (JP-A) No. 2012-78136 discloses technology that utilizes saturation current of a transistor provided in the buffer amplifier to diagnose malfunction in the above boosting circuit of a battery monitoring IC.
A circuit diagram of the battery monitoring system described in JP-A 2012-78136 that diagnoses the boosting circuit is illustrated in FIG. 4. In JP-A 2012-78136, a voltage that was boosted from a voltage V5 by a boosting circuit (not illustrated) or the voltage V5 is selectively supplied, as power supply voltage VCCUP, to the buffer amplifiers 30, 32. A circuit diagram of a specific example of the buffer amplifiers 30, 32 is illustrated in FIG. 5. The buffer amplifiers 30, 32 include: PMOS transistors 80, 82, 84, and 86; capacitor 88; and NMOS transistors 90, 92, and 94.
In the battery monitoring IC 120 illustrated in FIG. 4, in a case in which a power supply voltage VCCUP that was boosted by the boosting circuit is supplied as a drive voltage to the buffer amplifiers 30, 32, a voltage Vx1 output from the buffer amplifier 30 is the voltage V5, and a voltage Vy1 output from the buffer amplifier 32 is a voltage V4. An output Vout that is output from the comparison section 28 is the difference between the voltage V5 and the voltage V4 (V5−V4), the battery voltage of the battery cell Vc5.
However, in a case in which voltage V5 is supplied to the buffer amplifiers 30, 32 as a driving power supply voltage VCCUP, the voltage V5 input to the non-inverting input terminal of the buffer amplifier 30 and the power supply voltage VCCUP are substantially equivalent.
In a case in which the value of the voltage input to the non-inverting input terminal of the buffer amplifier 30 and the value of drive voltage of the buffer amplifier 30 are substantially equivalent, the MOS transistors in the buffer amplifier 30 (the PMOS transistors 80, 82, 84, and 86 and the NMOS transistors 90, 92, and 94 illustrated in FIG. 3) operate in the non-saturated region, the offset voltage in the output of the buffer amplifier 30 increases, and the voltage Vx1 output from the buffer amplifier 30 becomes V5−Vsat1. Further, since a potential difference between the voltage V4 input to the non-inverting input terminal and the power supply voltage VCCUP is present in the buffer amplifier 32, the output voltage of the buffer amplifier 32 becomes voltage V4. Thus, the output Vout output from the comparison section 28 (amplifier 40) becomes the difference between voltage V5−Vsat1 and the voltage V4 (V5−V4−Vsat1).
Accordingly, in a conventional battery monitoring system such as shown in FIG. 4, whether or not operation of the boosting circuit is normal is diagnosed by comparing an output Vout in a case in which a power supply voltage VCCUP supplied to the buffer amplifiers 30, 32 is a voltage that was boosted from a voltage V5 and an output Vout in a case in which the power supply voltage VCCUP is the voltage V5.
However, in a case in which the power supply voltage VCCUP of the buffer amplifiers 30, 32 is set to the voltage V5, and in a case in which the battery voltage of the battery cell Vc5 is low, the potential difference between the power supply voltage VCCUP and the voltage V4 is reduced, and the MOS transistors in the buffer amplifier 32 operate in the non-saturated region. Consequently, the offset voltage in the output of the buffer amplifier 32 increases, and the voltage Vy1 output from the buffer amplifier 32 becomes V4−Vsat2.
In a case in which the battery voltage of the battery cell Vc5 is low, the output Vout output from the comparison section 28 becomes the difference between the voltage V5−Vsat1 and the voltage V4−Vsat2 (V5−V4−Vsat1+Vsat2), and the variation in the output Vout due to the presence or absence of boosting by the boosting circuit decreases. Namely, in the method for diagnosing the boosting circuit described in JP-A 2012-78136, in a case in which the battery voltage of the battery cell Vc5 is low, the accuracy of diagnosing the boosting circuit may decrease.